Primary structure of PDC-109, a major protein constituent of bovine seminal plasma

The two major protein components of bovine seminal plasma, PDC-109 and BSP I, have been purified by gel filtration, partition chromatography and reverse-phase high performance liquid chromatography from an 86% ethanol precipitate of bovine seminal plasma ejaculate. The complete 109-residue amino acid sequence of PDC-109 has been established by automated Edman degradation of the intact peptide as well as its proteolytic digestion and cyanogen bromide cleavage fragments. The 12,774 dalton structure has two structurally similar domains of 38 and 41 amino acids, each containing two disulfide bonds.     

Highly purified particulate guanylate cyclase from rat lung: characterization and comparison with soluble guanylate cyclase

Guanylate cyclase was purified 1000-fold from washed rat lung particulate fractions to a final specific activity of 500 nmoles cyclic GMP produced/min/mg protein by a combination of detergent extraction and chromatography on concanavalin A-Sepharose, GTP-agarose, and blue agarose. Particulate guanylate cyclase has a molecular weight of 200 000 daltons, a Stokes radius of 48 A and a sedimentation coefficient of 9.4 while the soluble form has a molecular weight of 150 000 daltons, a Stokes radius of 44 A, and a sedimentation coefficient of 7.0. Whereas the particulate enzyme is a glycoprotein with a specific affinity for concanavalin A and wheat germ agglutinin, the soluble form of guanylate cyclase did not bind to these lectins. Purified particulate guanylate cyclase did not cross-react with a number of monoclonal antibodies generated to the soluble enzyme. While both forms of the enzyme could be regulated by the formation of mixed disulfides, the particulate enzyme was relatively insensitive to inhibition by cystine. With GTP as substrate both forms of the enzyme demonstrated typical kinetics, and with GTP analogues negative cooperativity was observed with both enzyme forms. These data support the suggestion that the two forms of guanylate cyclase possess similar catalytic sites, although their remaining structure is divergent, resulting in differences in subcellular distribution, physical characteristics, and antigenicity.     

Adaptive Functions of Vertebrate Molting Cycles

SYNOPSIS Cyclic epidermal cellular prohfeiation,with or withoutkeratinization is a vertebrate characteristic Such activityprobably obeys an autonomous rhythm which is legulated throughneuro humoral S)stcms in response to envnonmental (piox imate)stimuliand related to adaptive (ultimate) factors In seeking causeand effect lelationships, however, it becomes apparent thatthe same environmental parameter may be both an ultimate anda pioximate factor, the latter also regulating the rate of lesponseWith regard to molting in homoio'heims, tempeiatuie acts insuch a capacity in many species Peiiodic shedding of the outer epidermis in fish amphibiansand reptiles does not appear to be coirelated with seasonalfactors to the extent that avian and mammalian molts are The evolution of vertebrate molting cycles has amounted to theentraining of inherent epidermal C)cles with seasonal demandsby the organism itself and the environment,these demands actas regulating mechanisms Pieadapted structures such as feathersand hairs function collectively as plumage and pelage in theirvarious roles but separately in their growth and leplacementcycles which, however, are coordinated for maximum functionalefficiency Molting is also synchionized with the seasonal cycleaccording to the availability of energy resources and time tocomplete the essential functions (in addition to molting) Theevolved molting systems as manifested in the gieat variety ofpatterns and types in the vertebrates, may thus be legardedas almost individual responses to selective piessures actingon a umveisil vertebrate chaiacter The basic regulatoiy system involves the neuro hvpophyseal complexwhich contiols target endocrines affecting various functionswhich themselves influence epidermal mitosis and, ultimately,molting 1 he mechanism in its simplest form controls the animalsmetabolism through the thyroid acting independently in a permissivecapacity or synergistically with the adrenal and gonadal hormoneswhich are regulated directly and/or indirectly through negativefeedback     

Quantum theory of nerve excitation

Based on quantum transitions of membrane dipoles, the four fundamental properties of nerve impulse are derived in this paper: the all-or-none response, the strength-duration relation, refractoriness and refractory period and frequency modulation. Furthermore, the theory offers a physical mechanism for nerve excitation similar to a two-level ammonia maser. It also implies non-threshold excitation at elevated temperatures. The role of trimethylamine ions near the surface of a phospholipid membrane is briefly discussed to indicate a possible connection between theory and reality.     

Principles and applications of luminescence spectrometry coupled to liquid chromatographic techniques

An overview is presented of the physicochemical basis of luminescence, and its application to the detection of chemicals (drugs, biomedically important compounds, environmentally active substances) in liquid chromatographic systems.     

建兰根状茎增殖条件的研究

研究了建兰两个栽培品种的根状茎在固体及液体两种培养方式,以及培养基中有无激素和不同激素浓度配比对增殖及分化的影响。根状茎在液体培养基上的生长量都大于固体培养基上的生长量。根状茎在无激素的培养基上也能增殖。加入激素有促进作用。合适的激素浓度及配比因品种而异。     

P-glycoprotein: multidrug-resistance and a superfamily of membrane-associated transport proteins

The study of multidrug resistance (MDR) in tumor cell lines has led to the discovery of the plasma membrane P-glycoprotein (Pgp) molecule. This protein functions as an energy-dependent pump for the efflux of diverse anticancer drugs from MDR cells. It now appears that Pgp-mediated MDR tumor cells do occur in human cancers, and that they are likely to play a role in the ultimate response of patients to chemotherapy. Chemosensitizers, compounds able to reverse the MDR phenotype, have been identified and offer the exciting possibility of improving efficacy for some nonresponsive malignancies. Surprisingly, Pgp-like molecules can be found in evolutionarily distant species among both eukaryotes and prokaryotes. As a group, these proteins form a superfamily of ATP-dependent transport proteins. This finding has broad implications and provides new insights into how living organisms use this fundamental transport system to regulate the trafficking of diverse molecules across biological membranes.